420 Prof. Burdon-Sanderson and Mr. F. J. M. Page [Dec. 14, 



of a living part are correlated with other vital phenomena ; and for this 

 purpose, what is required is always to measure the electromotive force 

 between two points differing in function (in the physiological sense). 

 By the electrometer this measurement is made directly. In employing 

 the galvanometer a result is obtained which acquires no absolute value 

 until another investigation of very great difficulty has been gone virtually 

 through — that of measuring the electrical resistance of the tissues which 

 intervene between the two points investigated. In addition to this 

 obvious reason for preferring the measurement of tension difference to 

 the measurement of current, there are other reasons why the capillary 

 electrometer above described is specially adapted to the purposes of the 

 physiologist. One of the principal is that its indications are sensibly in- 

 stantaneous, on which account it is admirably suited for the investigation 

 of electrical changes of extremely short duration, and further that it is 

 portable and Httle liable to be injured by being moved from place to 

 place. A third advantage that it possesses is that it can be made and 

 graduated by the investigator himself. When in addition it is further 

 remembered that for every measurement made with the galvanometer at 

 least ten can be made in the same time with the electrometer with 

 greater accuracy, it does not appear unreasonable to anticipate that the 

 latter will in future be much used for physiological investigations. 



The second respect in which our method differs from those previously 

 employed is purely physiological. It had long been known as regards 

 the living animal body that the only tissues which are electromotive are 

 the nervous and muscular. All others behave, so far as has been ascer- 

 tained, as ordinary moist conductors. Investigated electroscopically they 

 exhibit, so long as they are in the living state, no variation of potential. 

 In the plant it is the same. An ordinary stem of a herbaceous plant 

 has the same potential as the soil in which it grows, or exhibits such 

 trifling variations that it may be said to be constant. In most of the 

 innumerable researches w^hich have been made in the domain of animal 

 electricity since the early discoveries of Du Bois-Eeymond, the method 

 has been adopted of comparing the electrical state of the part to be 

 investigated not with some other part of the organism outside of the 

 area of electrical change, and therefore possessing in relation to such 

 change a constant potential, but with some other part of the electrically 

 active organ itself. Thus, in the case of muscle, the cut surface has been 

 compared with the natural surface, the tendon with the muscular sur- 

 face, &c. These considerations led us to begin our investigation by com- 

 paring those parts of the leaf of Dionoea which appear to be the seat of 

 electrical change, not with other parts of the same organ, but with the 

 earth or with some other part of the same plant which we had previously 

 ascertained to be electrically indifferent and constant, i. e. free from 

 electrical vicissitudes. The way in which this was carried out will be 

 explained in the next section. 



